Inhibition of plastic crazing



United States Patent Ofiice 3,352,787 Patented Nov. 14, 1967 The present invention relates to improvements in the field of cleaners, and more specifically, to the cleaning of resinous materials which are subject to crazing.

Specifications for cleaning compounds, whether liquid or powder, frequently require that the cleaning material provide no deleterious effect on plastics. For example, government specifications for cleaning aircraft surfaces require that the cleaner shall be nonreactive with respect to Plexiglas surfaces such as those of the Windshields of aircraft. In fact, the government has issued a specific stress-crazing test which a material must meet in order to be acceptable.

In formulating cleaners for various purposes, including the cleaning of transparent acrylic base plastics, it would be highly desirable to include a significant amount of a non-ionic surfactant because of the excellent detergent properties of the non-ionic materials, and their relatively low cost. However, it was found that the use of many non-ionic surfactants created a crazing problem when applied to a stressed acrylic base plastic material.

I have now found that the crazing properties of these non-ionic surfactants can be overcome by the inclusion of ionic (anionic o1- cationic) surfactants in the same composition. These materials have the ability to not only inhibit the crazing tendencies characteristic of the nonionic surfactant but also improve the detergency.

An object of the present invention is to provide an improved composition for cleaning stressed acrylic base materials utilizing non-ionic surfactants without providing crazing of the surfaces.

A further object of the invention is to provide an improved cleaning composition adapted for cleaning transparent plastic surfaces including relatively large amounts of an inexpensive, non-ionic surfactant.

Still another object of the invention is to provide a method for cleaning stressed acrylic base surfaces without presenting the problem of crazing.

The compositions and method of the present invention are applicable to various physical forms of acrylic base plastics, including sheet material, filaments, fabrics and the like.

The cleaning compositions and method of the present invention are applicable to all types of light transmitting acrylic base polymers including polyacrylates and polymethacrylates. The invention has particular utility in connection with the cleaning of polymethyl methacrylate Plexiglas, a commercially available material which usually has a light transmission of 91 to 92%, a refractive index of about 1.49, a density of about 1.18, and a tensile strength of 7,000 to 9,000 p.s.i.

Certain non-ionic surfactant materials pose particularly troublesome crazing problems when applied to light transmitting, stressed acrylic based polymers. Among these are the materials known commercially as Triton which are non-ionic surface active agents prepared by the reaction of t-octylphenol or nonylphenol with ethylene oxide. These products are commercially described as alkyl aryl polyether alcohols or alkyl phenol ethers of polyethylene glycol. The number of ethylene oxide groups in the molecule may vary from about 1 to 30 and typically may contain 9 to 10 ethylene oxide groups (Triton X-l), or 12 to 13 ethylene oxide groups (Tn'ton X-l02).

Another series of nonionic surfactants which present corresponding ethylene oxide contents in crazing problems are those known commercially as Igepal, these being polyoxyethylated nonylphenols produced by the chemical reaction of nonylphenol with varying amounts of ethylene oxide ranging from 1% to 30 moles of ethylene oxide per mole of nonylphenol. The the final product range from about 23 to 86%. I

Still another class of materials which exhibit crazing problems in this connection are certain Pluronics which are block polymers consisting of a polyoxypropylene hydrophobic base and hydrophilic polyoxyethylene chains attached thereto.

As far as I have been able to determine, any anionic surfactant or any cationic surfactant material, when added in proper amounts is capable of neutralizing the tendency of the non-ionic materials to cause crazing of the light transmitting acrylic surface. Derivatives of carboxylic acids, including rosin and tall oil acids, are useful as are sulphuric esters derived from olefins and alcohols. Alkane sulfonates with and without intermediate linkages can also be employed. Mahogany and petroleum sulfonates, as well as other anionic surfactants such as phosphorus compounds, lignin derivatives, and the like can also be used. Particularly good results are obtained through the use of an alkyl aryl sulfonate (in the form of a sodium salt), the alkyl group containing from about 6 to 20 carbon atoms.

Similarly, the cationic surfactants may be either nonquaternary material such as nitriles, amines, or other nitrogen bases, as Well as the better known quaternary cationic materials.

Specific: examples of compositions embodying the improvements of the present invention will be found in a succeeding portion of this description. However, it should be recognized that the usable anionic and cationic surfactants are not limited by the examples, but can be any of the materials which fall into these designations. The invention contemplates that two or more anionic agents or two or more cationic agents can be used simultaneously. A more comprehensive discussion of anionic sur factants, and methods for their preparation will be found in the book, Surface Active Agents and Detergents, volume 2., by Schwartz, Perry and Berch (Interscience Publishers, 1958), pages 25 to 102. A similar discussion of cationic surfactants will be found in the same work, at pages 103 to 119.

While the proportions between the non-ionic and the ionic surfactant will vary over a wide range depending on the particular composition, it has been found that for most purposes, the amount of added anionic or cationic agent should be from to 5 times the amount of non-ionic surfactant present, and preferably from /5 to 2 times. It should be recognized, of course, that any cleaning composition embodying the combination of non-ionic and ionic surfactants may also include alkali metal tripolyphosph'ates and other polyphosphates, builders, sequestering agents, and the like.

The government approved test for stress crazing of acrylic base plastics requires that three specimens of sheet acrylic plastic be annealed by suspending in an oven maintained at :2 C. for 2 hours. At the end of the annealing period, the temperature of the specimens is reduced to room temperature at a maximum rate of 27i5 C. per hour. The annealed specimens are conditioned at room temperature for at least 7 days before use.

The'three specimens are then set up in cantilever fashion and carefully stressed to 3,000 lbs. per sq. in. outer fiber stress. After 10 minutes, the specimens are examined to insure that no crazing has occurred prior to the application of the cleaning compound. When the specimens are still under stress, an absorbent cotton swatch approximately inch square is placed on the tension side of the are rinsed with tap water and re-exarnined for crazing,-

cracking, or other attack.

Using this standard test, the following compositions, all containing a non-ionic surfactant and various amounts of. other materials were found to cause crazing:

Solution Percent Results 1 Water 90 Crazed.

Igepal CO 880 (30 ethylene oxide 5 group Triton N-128 (12-13 ethylene oxide 5 groups).

2 Water 95 Do.

Triton X-l02" (12-13 ethylene oxide 5 groups).

3 Water 95 Do.

Triton N-l28" 5 4 Water 95 Do.

Igepal CO 730" (15 ethylene oxide 5 groups).

5 Water 95 Do.

Triton (DI-l" 6 Water 95 D0.

Pluronlc L44 5 7 Water-.. 95 D0.

Pluroni P-75 5 8 Water 95 Do.

"Triton X 165 (16 ethylene oxide 5 groups).

9 Water 95 D0.

Triton X-205" (20 ethylene oxide 5 groups).

10 Water 95 Do.

"Triton X-305" (30 ethylene oxide 5 groups).

11 Water 95 Do.

Igepal CO 850" (20 ethylene oxide 5 groups).

12 Water 85 Do.

Tetrapotassium pyrophosphate 3 (TKPP Sodium metasllicate pentahydrate 5 Sodium gluconate 2 Triton X-l02 5 5 Sodium gluconate 2 Triton X102" 5 Butyl Cellosolve 2 14 Water 85 Do.

P 3 5 Triton X-165 7 15 #2fueloil 95 Do.

Triton X-45" (5 ethylene oxide 5 groups).

Inclusion of varying amounts of anionic and cationic surfactants in these compositions eliminated the crazing problem, as evidenced from the following examples:

benzyl ammonium chloride).

Solution Percent Results Water Do.

Triton X- "Duponol ME" (Lauryl alcohol sulfate).

Water Triton X-100" Sodium xylene sulfonate Water Marasperse N" (sodium lignosulfonate) no [O @0201 TKPP Sodium metasllicate pentahydrate. "Ultrawet DS Triton X-" drate. Ultrawet DS" Triton X-102" Waten.

omen COO c1100 09v 010 Q Ocn ow runicate pentahydrate. Ultrawet DS Triton X-100 Water Tetlr asgdium pyrophosphate PP Sodium metasilicate penta y- Dresinate T Sodium gluconate. "Triton X-lOO Water Sodium tripolyphosphate. Sodium metasilicate pentahydrate. Dresinate TX" Sodium glucouate. Triton X-102 By comparison of Example 2 with Examples 16 and 17, it will be noted that the substitution of the anionic agent for the corresponding amount of non-ionic agent entirely eliminated the crazing. .Similarly, by comparing Example 14 with Example 22 it will be seen that the substitution of a portion of the non-ionic surfactant with an anionic surfactant, all other things being constant, eliminated the crazing problem.

From the foregoing, it will be seen that compositions of the present invention eliminate the crazing problem which occurs when many non-ionic surfactants are applied in solution over a surface of a stressed, light transmitting acrylic base resin. It should also be noted that this crazing inhibition persists even though the compositions may also contain diverse materials such as phosphates, silicates, and salts of organic acids.

It should also .be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

I claim as my invention:

1. The method of washing a stressed acrylic base sheet which comprises applying thereto an aqueous solution of a polyethoxylated non-ionic surfactant which normally exhibits crazing properties when applied to stressed acrylic base sheets and from to 5 times the weight of the nonionic surfactant, of a water-soluble ionic surfactant selected from the group consisting of alkyl benzene sulfonates having from 6 to 20 carbons in the alkyl group, Xylene sulfonates, lignosulfonates, tall oil salts, petroleum sulfonates, lauryl alcohol sulfate, and diisobutyl phenoxy ethoxy dimethyl benzyl ammonium chloride.

2. The method of claim 1 wherein the non-ionic surfactant is a polyethoxylated alkyl phenol having from 8 to 9 carbons in the alkyl group and from 1 to 30 ethoxy groups.

3. The method of claim 1 wherein the non-ionic surfactant is a p0lyoxyethylene-polyoxypropylene copolymer.

4. The method of claim 1 wherein the ionic surfactant is an alkyl benzene sulfonate having from 6 to 20 carbons in the alkyl group.

5. The method of claim 1 wherein the ionic surfactant is a sodium lignosulfonate.

6. The method of claim 1 wherein the ionic surfactant is a sodium salt of tall oil.

7. The method of claim 1 wherein the ionic surfactant is a petroleum sulfonate.

8. The method of claim 1 wherein the ionic surfactant is lauryl alcohol sulfate.

9. The method of claim 1 wherein the ionic surfactant is diisobutyl phenoxy ethoxy dimethyl benzyl ammonium chloride.

10. The method of claim 1 wherein said aqueous solution contains about one weight percent sodium tripolyphosphate, about 5 weight percent sodium metasilicate, from about 1.5 to 2 weight percent of sodium salts of tall oil, from about 1 to 2.5 weight percent sodium g1uconate, and from about 5 to 5.5 weight percent of a polyethoxylated alkyl phenol having from 8 to 9 carbons in the alkyl group and from 12 to 13 ethoxy groups.

References Cited UNITED STATES PATENTS 2,292,097 8/1942 Vollmer 106-13 2,353,978 7/1944 Weber 10613 2,372,171 3/1945 Bennett 10613 2,726,962 12/1955 Iorio 106-43 2,878,188 3/1959 Callahan 252136 2,948,625 8/ 1960 MacKenzie 106-13 FOREIGN PATENTS 654,005 12/1962 Canada. 808,805 2/ 1959 Great Britain.

OTHER REFERENCES Surface Active Agents and Detergents, vol. II, Schwartz 20 et al., Interscience Publishers, Inc., NY. 1958, pp. 210, 

1. THE METHOD OF WASHING A STRESSED ARCYLIC BASE SHEET WHICH COMPRISES APPLYING THERETO AN AQUEOUS SOLUTION OF A POLYETHOXYLANTED NON-IONIC SURFACTANT WHICH NORMALLY EXHIBITS CRAZING PROPERTIES WHEN APPLIED TO STRESSED ACRYLIC BASE SHEETS AND FROM 1/20 TO 5 TIMES THE WEIGHT OF THE NONIONIC SURFACTANT, OF A WATER-SOLUBLE IONIC SURFACTANT SELECTED FROM THE GROUP CONSISTING OF ALKYL BENZENE SULFONATES HAVING FROM 6 TO 20 CARBONS IN THE ALKYL GROUP, XYLENE SULFONATE, LIGOSULFONATES, TALL OIL SALTS, PETROLEUM SULFONATES, LAURLY ALCOHOL SULFATE, AND DIISOBUTYL PHENOXY ETHOXY DIMETHYL BENZYL AMMONIUN CHLORIDE. 